path: root/Documentation/technical/api-sha1-array.txt
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authorJeff King <>2011-09-13 21:57:34 (GMT)
committerJunio C Hamano <>2011-09-14 18:44:05 (GMT)
commit163ed566db7fd0f286413040e368324a59c642f9 (patch)
tree6984d630569f83e3447dc61716a037b99206d78a /Documentation/technical/api-sha1-array.txt
parent6859de45a94ec0e88703250d9d4df64a09042333 (diff)
add sha1_array API docs
This API was introduced in 902bb36, but never documented. Let's be nice to future users of the code. Signed-off-by: Jeff King <> Signed-off-by: Junio C Hamano <>
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+sha1-array API
+The sha1-array API provides storage and manipulation of sets of SHA1
+identifiers. The emphasis is on storage and processing efficiency,
+making them suitable for large lists. Note that the ordering of items is
+not preserved over some operations.
+Data Structures
+`struct sha1_array`::
+ A single array of SHA1 hashes. This should be initialized by
+ assignment from `SHA1_ARRAY_INIT`. The `sha1` member contains
+ the actual data. The `nr` member contains the number of items in
+ the set. The `alloc` and `sorted` members are used internally,
+ and should not be needed by API callers.
+ Add an item to the set. The sha1 will be placed at the end of
+ the array (but note that some operations below may lose this
+ ordering).
+ Sort the elements in the array.
+ Perform a binary search of the array for a specific sha1.
+ If found, returns the offset (in number of elements) of the
+ sha1. If not found, returns a negative integer. If the array is
+ not sorted, this function has the side effect of sorting it.
+ Free all memory associated with the array and return it to the
+ initial, empty state.
+ Efficiently iterate over each unique element of the list,
+ executing the callback function for each one. If the array is
+ not sorted, this function has the side effect of sorting it.
+void print_callback(const unsigned char sha1[20],
+ void *data)
+ printf("%s\n", sha1_to_hex(sha1));
+void some_func(void)
+ struct sha1_array hashes = SHA1_ARRAY_INIT;
+ unsigned char sha1[20];
+ /* Read objects into our set */
+ while (read_object_from_stdin(sha1))
+ sha1_array_append(&hashes, sha1);
+ /* Check if some objects are in our set */
+ while (read_object_from_stdin(sha1)) {
+ if (sha1_array_lookup(&hashes, sha1) >= 0)
+ printf("it's in there!\n");
+ /*
+ * Print the unique set of objects. We could also have
+ * avoided adding duplicate objects in the first place,
+ * but we would end up re-sorting the array repeatedly.
+ * Instead, this will sort once and then skip duplicates
+ * in linear time.
+ */
+ sha1_array_for_each_unique(&hashes, print_callback, NULL);